We have developed several novel systems to study N-myc function and regulation. In this context, we have five highly interrelated goals. We will characterize the molecular elements that regulate N-myc expression. In particular, we will characterize the transcriptional control elements responsible for interleukin-7 mediated regulation of N-myc transcriptional attenuation in pre-B cells as well as those responsible for down-regulation of N-myc transcription in mature B cells and in pre-B cell tumors that arose as a result of deregulated N-myc expression. We also will seek to define additional elements that regulate N-myc expression during murine development. We will study N-myc protein function by comparing N-myc to other myc proteins with respect to DNA binding-site preference and affinity, structural requirements for sequence-specific binding, potential interactions with known or novel proteins, and ability to activate transcription. We also will search for genetic targets of the N-myc protein through the use of several strategies that exploit novel cell lines that we have or will develop including IL-7-dependent lines or lines in which endogenous N-myc genes have been eliminated. We will study the role of N-myc in murine development by detailed analyses of the embryonic lethal phenotype of mice homozygous for a mutation that disrupts the N-myc gene (generated in our laboratory). We will extend this approach by complementing the non-functional genes with various forms of the N-myc gene supplied by transgenic donors created for this purpose. ES cells lacking the N-myc gene will be analyzed for ability to contribute to somatic chimeric mice. We will employ novel strategies to determine when myc genes and individual myc family members arose in evolution. Finally, we will extend the types of studies listed in aims 2 and 3 to the L-myc gene.